Upstream adaptive modulation in a communications system

ABSTRACT

A system and method for providing upstream adaptive modulation. Burst parameters associated with a range of data interval usage codes (IUCs) are defined. Each of the data IUCs has a different modulation order and forward error correction (FEC). The SNR and codeword error rate for each satellite modem in the network are monitored. The data IUCs are dynamically assigned to different satellite modems within an upstream channel based on SNR and/or codeword error rate to enable each of the satellite modems in the upstream channel to achieve maximum bandwidth efficiency during upstream data transmissions. Bandwidth requests are received from the satellite modems and granted. The grant includes the assigned data IUC. The data bursts received in the upstream channel are each processed using the parameters from the assigned IUC for each of the satellite modems sending data in the upstream channel. When any of the satellite modems&#39; SNR and/or codeword error rate changes, the data IUC for that satellite modem is changed accordingly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/352,251, filed on Jan. 28, 2003, titled “Upstream Adaptive Modulationin DOCSIS Based Applications”, which is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to broadband communicationssystems. More particularly, the present invention is related tobroadband communications systems that use Data Over Cable ServiceInterface Specification (DOCSIS) or any of its derivatives.

2. Background Art

In DOCSIS related broadband communications architectures, data istransferred between a central location and many remote subscribers. Thecentral location may be referred to as a headend for cable systems, awireless access termination system (WATS) for broadband terrestrialfixed wireless systems, or a satellite gateway for two-way satellitesystems. Subscriber equipment may be referred to as a cable modem (CM)for cable systems, a wireless modem (WM) for broadband terrestrial fixedwireless systems, or a satellite modem (SM) for two-way satellitesystems.

BACKGROUND ART

In a two-way satellite system, the communication path from the satellitegateway to the SM is called the downstream and the communication pathfrom the SM to the satellite gateway is called the upstream. In standardDOCSIS based systems, the upstream is implemented in a time divisionmultiple access (TDMA) protocol with a fixed modulation type and forwarderror correction (FEC) coding rate. Such signals have a fixed spectralefficiency in bits per second/Hertz (bps/Hz). Signal parameters such asmodulation type, FEC coding type, and FEC coding rate determine thesignal-to-noise ratio (SNR) required for the SM to have error-free orquasi error-free operation in a given channel. There is an inherenttrade-off between receiver parameters that allow for high throughput(high order modulation, high FEC code rates) and those that allow thesignal to be reliably received at low SNRs, but with a lower throughput(low order modulations, robust low code rate FECs).

In many real world environments, subscribers experience a wide range ofpath losses and channel degradations. For example, in the case of asatellite based system where a downstream spot beam is broadcasting toSMs that are located over a wide geographic area, various degradations,such as localized rainfall, partial obstructions, antenna misalignments,etc., cause the upstream signal power levels and SNRs received at thesatellite gateway from individual subscribers to vary significantly.Terrestrial wireless and cable systems may experience the samephenomenon for different reasons.

Current DOCSIS based systems operate with parameters that allow theworst case subscriber to obtain service with a given probability ofsuccess. Subscribers that could otherwise transmit upstream data at ahigher rate are penalized by the presence of disadvantaged subscribers.

Thus, what is needed is a system and method of dynamically assigningdata traffic with different modulation orders and FEC parameters todifferent SMs within the same upstream channel, referred to as “upstreamadaptive modulation (US-AM).” What is also needed is a system and methodthat implements US-AM in a manner that enables non US-AM enabled SMs toefficiently continue operation

BRIEF SUMMARY OF THE INVENTION

The present invention solves the above-mentioned problems by providing asystem and method for dynamically assigning data traffic with differentmodulation orders and FEC parameters to different satellite modems (SMs)within the same upstream channel. As previously stated, this is alsoreferred to as upstream adaptive modulation. The present inventionaccomplishes this by extending existing DOCSIS mechanisms for requestingbandwidth and defining data burst parameters. The extensions allow thesatellite gateway to instruct each individual SM to use burst parametersthat achieve the maximum bandwidth efficiency possible under theconstraints of the system capabilities, channel conditions andrequirements on received signal quality metrics. This results in acombination of improved channel capacity, increased throughput, andimproved coverage.

Briefly stated, the present invention is directed to a system and methodfor providing upstream adaptive modulation. Burst parameters associatedwith a range of data interval usage codes (IUCs) are defined. Each ofthe data IUCs has a different modulation order and forward errorcorrection (FEC). The SNR and codeword error rate for each satellitemodem in the network are monitored. The data IUCs are dynamicallyassigned to different satellite modems within an upstream channel basedon SNR and/or codeword error rate to enable each of the satellite modemsin the upstream channel to achieve maximum bandwidth efficiency duringupstream data transmissions. Bandwidth requests are received from thesatellite modems and granted. The grant includes the assigned data IUC.The data bursts received in the upstream channel are each processedusing the parameters from the assigned IUC for each of the satellitemodems sending data in the upstream channel. When any of the satellitemodems' SNR and/or codeword error rate changes, the data IUC for thatsatellite modem is changed accordingly.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art(s) to makeand use the invention.

FIG. 1 is a high level block diagram of an exemplary broadband two-waysatellite communications system in accordance with embodiments of thepresent invention.

FIG. 2 is a simplified flow diagram of a standard DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite modem.

FIG. 3 is a simplified flow diagram of a standard DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite gateway.

FIG. 4 is a flow diagram of a modified DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite modem according to an embodiment of the present invention.

FIG. 5 is a graph illustrating upstream operating points associated withupstream adaptive modulation IUCs according to an embodiment of thepresent invention.

FIG. 6 is a flow diagram of a modified DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite gateway according to an embodiment of the present invention.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawings in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those skilled inthe art(s) with access to the teachings provided herein will recognizeadditional modifications, applications, and embodiments within the scopethereof and additional fields in which the present invention would be ofsignificant utility.

Overview

FIG. 1 is a high level block diagram of an exemplary broadband two-waysatellite communications system 100 in accordance with embodiments ofthe present invention. Although the present invention is described usinga broadband two-way satellite communications system, the presentinvention is also applicable to other broadband communications systems.Such systems may include, but are not limited to, broadband cablesystems and broadband terrestrial fixed wireless systems. Broadbandtwo-way satellite communications system 100 enables voicecommunications, video and data services based on a bi-directionaltransfer of packet-based traffic between a satellite gateway 102 and oneor more satellite modems (SM), such as satellite modems 104 and 106, viaa satellite 112. Satellite 112 is a vehicle or platform designed toorbit the earth. Satellite 112 contains electronic devices fororiginating and/or relaying telecommunications, data, etc. betweensatellite gateway 102 and one or more satellite modems, such as SMs 104and 106. For example, in an embodiment of the present invention,satellite 112 receives packet-based traffic from satellite gateway 102and relays such traffic to one or more satellite modems, such assatellite modems 104 and 106. Satellite 112 also receives packet-basedtraffic from satellite modems, such as satellite modems 104 and 106, andsends such traffic to satellite gateway 102. Although broadband two-waysatellite communications system 100 is shown with only two satellitemodems, any number of satellite modems may be included in the broadbandtwo-way satellite communications system 100 of the present invention.

Bi-directional transfer of packet-based traffic is achieved usingantennas, such as antennas 108, 109, 110, and 111, and transceivers 114,116 and 118. Satellite 112 is coupled to antennas 111 for receiving andtransmitting information. Antenna 108 is coupled to satellite gateway102 via transceiver 114 for transmitting/receiving packet-based trafficto/from SMs 104 and 106, respectively, via satellite 112. Antennas 109and 110 are coupled to SMs 104 and 106 via transceivers 116 and 118,respectively, for transmitting/receiving packet-based traffic to/fromsatellite gateway 102, via satellite 112. The communication path fromsatellite gateway 102 to satellite modems 104 and 106 is called thedownstream. The communication path from satellite modems 104 and 106 tosatellite gateway 102 is called the upstream.

Satellite gateway 102 is a central distribution point for broadbandtwo-way satellite communications system 100. Satellite gateway 102manages the upstream and downstream transfer of data between satellitegateway 102 and satellite modems, such as satellite modems 104 and 106,via satellite 112. Satellite gateway 102 broadcasts informationdownstream to satellite modems 104 and 106 as a continuous transmittedsignal in accordance with a time division multiplexing (TDM) technique.Satellite gateway 102 also controls the upstream transmission of datafrom satellite modems 104 and 106 to satellite gateway 102 by assigningto each satellite modem (104 and 106) slots within which to transferdata in accordance with a time domain multiple access (TDMA) technique.Thus, each satellite modem (104 and 106) sends information upstream asshort burst signals during a transmission opportunity allocated bysatellite gateway 102.

Each of satellite modems 104 and 106 operates as an interface to a userdevice (not shown). User devices may include, but are not limited to,personal computers, data terminal equipment, telephony devices,broadband media players, personal digital assistants, network-controlledappliances, or any other device capable of transmitting or receivingdata. Satellite modems 104 and 106 perform the functions necessary toconvert downstream signals received over broadband two-way satellitecommunications system 100 into data packets for receipt by an attacheduser device. Satellite modems 104 and 106 perform the functionsnecessary to convert data signals received from the user devices intoupstream burst signals suitable for transfer over broadband two-waysatellite communications system 100.

In exemplary broadband two-way satellite communications system 100,satellite modems 104 and 106 operate in formats that adhere to theprotocols set forth in the DOCSIS specification as well as proprietaryprotocols that extend beyond the DOCSIS specification. Additionally,satellite gateway 102 operates to transmit, receive and process datatransmitted to it in accordance with the protocols set forth in theDOCSIS specification and can also operate to transmit, receive andprocess data packets that are formatted using proprietary protocols thatextend beyond those provided by the DOCSIS specification. The manner inwhich satellite modems 104 and 106 operate to transmit data will bedescribed in further detail herein. The manner in which satellitegateway 102 operates to receive and process data will also be describedin further detail herein. The following description will now concentrateon the upstream transfer of data from satellite modems 104 and 106 tosatellite gateway 102, via satellite 112.

In DOCSIS based systems, the upstream traffic flow of a given SM(104/106) is assigned one or more service IDs (SIDs) by satellitegateway 102. Many SMs share an upstream channel by transmitting burstswithin assigned burst times for a given SM (104/106). Burst times areassigned by a MAP message sent in the downstream. Each burst intervalassigned in the MAP message has an associated SID that identifies theupstream traffic flow of a given SM (104/106) and an Interval Usage Code(IUC) that identifies the burst type.

In the DOCSIS protocol, several well known IUC numbers are associatedwith various defined burst types. An IUC=1 is defined as a requestaccess (RA) burst. An IUC=2 is defined as a request/data burst. An IUC=3is defined as an initial maintenance. An IUC=4 is defined as a stationmaintenance. An IUC=5 is defined as a short data burst for standardDOCSIS. An IUC=6 is defined as a long data burst for standard DOCSIS. AnIUC=9 is defined as a short data burst for an advanced physical layer(PHY) version of standard DOCSIS. And an IUC=10 is defined as a longdata burst for an advanced physical layer (PHY) version of standardDOCSIS. There are also several reserved IUCs for future use as otherdata types.

The parameters associated with different IUCs are defined at the Gatewayand communicated to the SM by means of an upstream channel descriptor(UCD) message. UCD messages are sent periodically in the downstreamdirection from satellite gateway 102 to the SM (104/106). For satelliteapplications, UCD messages must be modified to properly describesatellite upstream channel parameters. Modifications include, but arenot limited to, adding parameters describing the inner code rate, turbo(or other inner code) block size, number of tailing symbols in a innercode word, etc., all of which are well known to those skilled in therelevant art(s). Implementation of the present invention assumes thatthe UCDs have been properly modified to describe the relevant satelliteupstream parameters.

In standard-DOCSIS, data is both requested and granted in terms ofmini-slots. In standard DOCSIS, a mini-slot is defined as a factor oftwo multiple of 6.25 microseconds. The factor used (and hence themini-slot time duration) is programmable and can vary in differentrealizations. When a SM transmits data, the selection of a short vs.long data burst type is determined solely by the length of the grant inmini-slots. If the number of granted mini-slots exceeds a programmablethreshold, a long data burst type is used. If the grant does not exceedthis threshold, a short data burst type is used. This threshold isdefined at satellite gateway 102 and communicated to SMs (104/106) aspart of the UCD message. Thus, with standard DOCSIS, only two data bursttypes, short and long, are used by SMs, such as SMs 104 and 106, totransmit data upstream.

Transmission of an Upstream Data Packet Using Standard DOCSIS

FIG. 2 is a simplified flow diagram of the current standard-DOCSISprocess for the transmission of an upstream data packet from theperspective of a satellite modem. To more clearly illustrate contrastingmechanisms between the current process and the present invention,details of the DOCSIS error recovery mechanisms are omitted. Also,DOCSIS features such as fragmentation and unsolicited grant service(UGS) are not enabled. The process begins with step 202, where theprocess immediately proceeds to step 204.

In step 204, the satellite modem (104/106) receives upstream channel andburst type parameters from an upstream channel descriptor message andregisters with the network prior to initializing any data transfer.Upstream data transfer is initialized when an Ethernet frame is input tothe satellite modem (104/106) from the customer premises equipment(CPE). CPE is equipment at the end user's premises, which may beprovided by an end user or a service provider. The process then proceedsto step 206.

In step 206, the satellite modem (104/106) determines the media accesscontrol (MAC) header and appends the MAC header to the data packet thatis to be transmitted. The satellite modem (104/106) has knowledge of thetotal number of bytes (Ethernet bytes plus DOCSIS header overhead) thatare to be transmitted. The process then proceeds to step 208.

In step 208, the satellite modem (104/106) determines the number ofmini-slots required to transmit the data packet. The satellite modem(104/106) calculates the number of mini-slots required as a function of(1) the number of bytes to be transmitted; (2) the mini-slot size; (3)the symbol rate; (4) the coding and modulation parameters to be used;and (5) burst overhead parameters such as preamble length and guardtime. Implicit in this calculation is the knowledge of whether the shortdata or long data parameters are to be used. As was indicatedpreviously, in standard DOCSIS this determination is made solely onwhether the number of mini-slots in the request is above or below aprogrammable threshold. Both the satellite gateway (102) and satellitemodem (104/106) are aware of this threshold. In an alternativeembodiment, the satellite modem (104/106) may use a precalculated lookup table to determine the number of mini-slots required to transmit thedata packet. The process then proceeds to step 210.

In step 210, the satellite modem (104/106) makes a bandwidth request forthe proper number of mini-slots. This request can be made in a number ofways. For example, the request can be made in a multi-cast requestaccess burst slot, in a uni/cast request access burst slot, as part of apiggyback request made from a previously granted data burst, in abandwidth request field of a modified range request, or in some othermanner to be defined in the future. The satellite modem (104/106)records the time that the request was made. The process then proceeds tostep 212.

In step 212, the satellite modem (104/106) waits for a data grant to bereceived in a MAP message associated with the upstream being used. Thesatellite modem (104/106) may perform other tasks unrelated to theprocessing of the data packet during the wait period. The satellitemodem (104/106) will wait until either: (a) it receives a MAP messageindicating a data grant; or (b) it receives a MAP message where theacknowledge time is greater than the time of the request. The processthen proceeds to decision step 214.

In decision step 214, it is determined whether the satellite modem(104/106) has received a data grant or an acknowledge time that isgreater than the time in which the request was made. If it is determinedthat the satellite modem (104/106) has received an acknowledge time thatis greater than the time in which the request was made without firstreceiving a data grant, then the satellite gateway (102) was unable togrant the bandwidth request for the satellite modem (104/106). This mayoccur for a variety of reasons which are well known to those skilled inthe relevant art(s). The process then proceeds to step 216.

In step 216, the satellite modem (104/106) may request the bandwidthagain, flush the packet, or perform other error recovery mechanisms.

Returning to decision step 214, if it is determined that the satellitemodem (104/106) received a data grant, the process proceeds to decisionstep 218.

In decision step 218, it is determined whether the number of mini-slotsin the grant are adequate to transmit the data packet. If it isdetermined that the number of mini-slots are inadequate, andfragmentation is not enabled, the grant is unused and the processproceeds back to step 212, where the satellite modem (104/106) waits foranother standard DOCSIS data grant.

Returning to decision step 218, if it is determined that the number ofmini-slots granted are adequate to transmit the data packet, the processthen proceeds to step 220.

In step 220, the data packet is transmitted to the gateway (102) in theproper burst interval and processing of the packet by the satellitemodem (104/106) is completed.

FIG. 3 is a simplified flow diagram of a standard DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite gateway (102). The process begins with step 302 andimmediately proceeds to step 304.

In step 304, the satellite gateway (102) defines parameters for standardDOCSIS data IUCs and sends these parameters to the satellite modems (104and 106) via an upstream channel descriptor (UCD). The process thenproceeds to step 306.

In step 306, the satellite gateway (102) receives a request forbandwidth from a given satellite modem (104/106). This request isreferenced to a known SID of the satellite modem (104/106), and is inunits of mini-slots. The process then proceeds to step 308.

In step 308, the satellite gateway 102 grants the request in theappropriate MAP message. The grant in the MAP message contains the SID,the offset, and the IUC of the grant. The start time and duration of thegrant are inferred from the start time of the overall map and the offsetof the other grants in the MAP message. The IUC for the data packetcorresponds to either a long or short burst type IUC for data dependingon the number of mini-slots in the grant. The process then proceeds tostep 310.

In step 310, the satellite gateway (102) then waits for the data burstto arrive in the specified grant interval. The process then proceeds tostep 312.

In step 312, the gateway (102) processes the received burst usingparameters appropriate for either long or short data depending on thetype of burst used.

In the previous description of the transmission process, for a givensize data burst there is no mechanism that enables different satellitemodems to use different burst parameters such as coding rate ormodulation type. With the standard or advanced physical layer version ofDOCSIS, there are only two IUCs for transmitting data. The two IUCs areassociated with short and long data, respectively. The parametersassociated with short and long data are based on mini-slot size only.Thus, the burst parameters are fixed for a given upstream configuration,requiring all satellite modems to operate at the same bandwidthefficiency.

Upstream Adaptive Modulation

The present invention implements adaptive modulation by dynamicallyassigning data traffic with different modulation orders and FECparameters to different satellite modems (SMs) within the same upstreamchannel. The present invention accomplishes this by extending existingDOCSIS mechanisms for requesting bandwidth and defining data burstparameters. The extensions allow the satellite gateway to instruct eachindividual SM to use burst parameters that achieve the maximum bandwidthefficiency possible under the constraints of the system capabilities,channel conditions and requirements on received signal quality metrics.This results in a combination of improved channel capacity, increasedthroughput, and improved coverage.

The present invention extends the concept of data burst transmissionsbased solely on short and long data. Instead, the present uses aplurality of IUCs for transmitting data. Each IUC has associated with ita plurality of parameters that achieve different bandwidth efficiencies.Upon receiving a request for bandwidth from a SM, the satellite gatewaywill assign an IUC to the SM based on the SM's SNR, codeword error rate,etc, to enable the SM to achieve the maximum bandwidth efficiencypossible for that individual SM. This enables different satellite modemswithin the same upstream channel to have different modulation orders andFEC parameters.

FIG. 4 is a flow diagram 400 of a modified DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite modem according to an embodiment of the present invention. Theinvention is not limited to the description provided herein with respectto flow diagram 400. Rather it would be apparent to person(s) skilled inthe relevant art after reading the teachings provided herein that otherfunctional flow diagrams are within the scope of the present invention.The process begins with step 402, where the process immediate proceedsto step 404.

In step 404, prior to initializing any data transfer, the satellitemodem (104/106) receives upstream channel parameters via the upstreamchannel descriptor messages. The present invention requires that aplurality of data IUCs be defined. Different data IUCs are assignedunique parameter sets. A key objective of the parameter set definitionis to obtain operating points spaced over a desired range.

FIG. 5 is a graph illustrating upstream operating points associated withupstream adaptive modulation IUCs according to an embodiment of thepresent invention. FIG. 5 shows a plurality of predefined parameter setsfor each newly defined set of IUCs spaced over a desired range ofoperating points. For example, parameter set 1 for IUC=K1 requires avery small SNR to be able to operate without errors, but the bandwidthefficiency is low. Parameter set N for IUC=KN has a very high bandwidthefficiency, but requires a very high SNR to be able to operate withouterrors. Important parameters that set bandwidth efficiency and determinesignal to noise ratio requirements include, but are not limited to,modulation type, inner code rate, outer code rate (or equivalently outercode Reed-Solomon k and T values), inner code block size, and inner codetailing symbols (flush symbols). Each parameter set shown in FIG. 5includes a set of these important parameters. One skilled in therelevant art(s) would know that other parameters may also be used indefining the parameter sets for each unique IUC. Note in particular thatdifferent IUCs can still be defined for short and long data bursts.

Thus for the present invention, the upstream transmission of data is notbased solely on two IUCs for short and long data bursts, respectively.To the contrary, the upstream transmission of data is based on aplurality of newly defined IUCs having unique parameter sets thatprovide the capability for each individual SM transmitting on a singleupstream channel to use burst parameters that achieve the maximumbandwidth efficiency possible for each SM. This enables the use ofhigher code rates, thereby reducing the amount of mini-slots granted.With each SM being able to transmit data based on its own capabilitiesrather than the capabilities of the worst case SM, improved channelcapacity, higher throughput and improved coverage results. Also, whenconditions change for any one SM, such as, for example, a decrease inSNR resulting from a rain storm or the like, the system adapts byassigning that SM a different IUC that accommodates for the decrease inSNR.

Returning to FIG. 4, the process then proceeds to step 406. In step 406,upstream data transfer is initiated when an ethernet frame is input tothe satellite modem from the CPE. The process then proceeds to step 408.

In step 408, the satellite modem (104/106) determines and appends theMAC header that is to be transmitted along with the packet. Thesatellite modem (104/106) has knowledge of the total number of bytes(ethernet bytes plus DOCSIS header overhead) that are to be transmittedupstream.

In step 410, the satellite modem (104/106) makes a bandwidth requestdirectly for the appropriate number of bytes (i.e., the units of therequest are in bytes and not mini-slots). Alternatively, the satellitemodem (104/106) may request bandwidth in mini-slots using parametersassociated with some fixed and pre-defined IUC. The satellite gateway(102) would then use knowledge of the parameters of this IUC todetermine the number of bytes requested, thus, obtaining the equivalentinformation. As in the standard DOCSIS case, the bandwidth request maybe made in a multi-cast request access burst slot, in a uni-cast requestaccess burst slot, as part of a piggyback request made in a data burst,in a bandwidth request field of a modified range request, or in someother manner to be determined at a future time. The satellite modem(104/106) makes note of the time that the request was made. The processthen proceeds to step 412.

In step 412, the satellite modem (104/106) waits for a data grant to bereceived in a map message associated with the upstream being used. Thesatellite modem (104/106) realizes that it may be granted a slot on anyof the defined data IUCs. As in standard DOCSIS, the grant in the map isdefined in mini-slots. The satellite modem (104/106) will exit the waitstate when it receives: (a) a data grant for any one of the data IUCs;or (b) a map message where the acknowledge time in the map is greaterthan the time of the request. If the acknowledgment time in the mapmessage is greater than the request time, a request is not granted andthe process proceeds to step 414.

In step 414, the satellite gateway (102) is not able to grant thesatellite modem's bandwidth request. This may occur for a variety ofreasons, which are well known to those skilled in the relevant art(s).At this time, the satellite modem (104/106) may request bandwidth again,flush the packet, or perform other error recovery mechanisms.

Returning to step 412, if a data grant is received, the process thenproceeds to decision step 416. In decision step 416, the satellite modem(104/106) checks the grant to ensure that the number of mini-slots isadequate to transmit the package. There are several possible data grantIUCs, and a required number of mini-slots is potentially different foreach IUC type. Hence, this calculation or result from a lookup tablemust consider the IUC of the data grant. If the number of mini-slots isnot adequate and fragmentation is not enabled, the grant is unused andthe satellite modem returns to the wait state in step 412.

Returning to decision step 416, if the data grant contains the necessarynumber of mini-slots, the process proceeds to step 418.

In step 418, the data packet is transmitted to the satellite gateway(102) using the burst parameters associated with the IUC granted by thesatellite gateway (102). The satellite modem processing of this packetis now complete.

FIG. 6 is a flow diagram 600 of a modified DOCSIS process for thetransmission of an upstream data packet from the perspective of asatellite gateway according to an embodiment of the present invention.The invention is not limited to the description provided herein withrespect to flow diagram 600. Rather it would be apparent to person(s)skilled in the relevant art after reading the teachings provided hereinthat other functional flow diagrams are within the scope of the presentinvention. The process begins with step 602, where the process immediateproceeds to step 604.

In step 604, prior to the start of processing, the satellite gateway(102) defines burst parameters associated with a range of data IUCs. Aspreviously stated, each defined IUC is associated with a uniqueparameter set that includes modulation type, FEC coding type, and FECcoding rate. The burst parameter definitions of the data IUCs are sentto the satellite modems (104/106) via UCD messages. The process thenproceeds to step 606.

In step 606, as part of the registration process, and as an ongoingtask, the satellite gateway (102) monitors the received SNR and/orpacket error performance of each SM (104/106) on the network and assignseach SM (104/106) to use burst parameters associated with a unique IUC.This assignment can vary over time as the received SNR, packet errorrate performance, or other metrics from a given SM vary. For example, ifthe SNR for a SM goes down, possibly due to rain or other bad weatherconditions, and the satellite gateway starts seeing errors, then thesatellite gateway will drop the SM (104/106) down to a lower IUC or anIUC that requires a lower SNR. When the SM's SNR and codeword error ratebegin to improve, the satellite gateway (102) will bump the SM (104/106)up to a higher IUC, accordingly. The process then proceeds to step 608.

In step 608, the satellite gateway (102) receives a request forbandwidth from a given satellite modem (104/106). This request isreferenced to a known SID assigned to the satellite modem (104/106), andis in units of bytes. The process then proceeds to step 610.

In step 610, the gateway calculates the number of mini-slots necessaryfor the bandwidth request given the burst parameters associated with thesatellite modem's assigned IUC. Note that a higher SNR requires fewermini-slots to be granted. A lower SNR requires more mini-slots to begranted. Thus, with the present invention, the satellite gateway (102)is granting fewer mini-slots by assigning IUCs based on SNR and codeworderror rate. Alternatively, the satellite gateway (102) may utilize aprecalculated lookup table to determine the number of mini-slots. Theprocess then proceeds to step 612.

In step 612, the satellite gateway (102) grants the request in theappropriate MAC message. The MAC message is in the standard DOCSISformat. The SID and IUC of the grant is specified, along with offsetinformation by which to infer the number of mini-slots of the grant. Theprocess then proceeds to step 614 where the gateway waits for the databurst to arrive in the specified grant interval. The process thenproceeds to step 616.

In step 616, the gateway (102) processes the received burst usingparameters appropriate for the IUC that it specified in the burst. Thus,the present invention implements upstream adaptive modulation within thecontext of a DOCSIS-based satellite or other system. It allows eachsatellite modem to individually be assigned burst parameters thatoptimize the SM's bandwidth efficiency given the SM's operationalenvironment.

CONCLUSION

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. While the invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and detail maybe made therein without departing from the spirit and scope of theinvention.

1. An upstream modulation method for a communications system,comprising: defining burst parameters associated with a range of datainterval usage codes (IUCs); monitoring signal-to-noise ratio (SNR) andcodeword error rates for modems connected to a network; and dynamicallyassigning the data IUCs to the modems within an upstream channelaccording to at least one of the SNR and the codeword error rate toenable each of the modems in the upstream channel to achieve maximumbandwidth efficiency during upstream data transmissions.
 2. The methodof claim 1, further comprising: receiving bandwidth requests from themodems; granting the bandwidth requests, wherein the grant includes theassigned data IUC; and processing data from received bursts usingparameters from the assigned data IUCs for each of the modems sendingdata in the upstream channel.
 3. The method of claim 2, furthercomprising changing an assigned data IUC for any one of said modems toadapt to changes in measured SNR and/or codeword error rate.
 4. Themethod of claim 2, further comprising determining the number ofmini-slots needed prior to granting said request for bandwidth.
 5. Themethod of claim 1, further comprising changing the data IUC for anymodem to adapt to changes in the modem's SNR and/or codeword error rate.6. The method of claim 1, wherein said burst parameters includemodulation type, forward error correction (FEC) coding type, and FECrate.
 7. The method of claim 4, wherein each of said data IUCs has aunique parameter set.
 8. The method of claim 1, wherein each of the dataIUCs includes a modulation order and forward error correction (FEC)parameters for the upstream channel.
 9. An upstream modulation systemfor broadband communications, comprising: means for defining burstparameters associated with a range of data interval usage codes (IUCs);means for monitoring signal-to-noise ratio (SNR) and codeword errorrates for modems in a network; and means for dynamically assigning thedata IUCs to the modems within an upstream channel according to at leastone of the SNR and the codeword error rate to enable each of the modemsin the upstream channel to achieve bandwidth efficiency during upstreamdata transmissions.
 10. The system of claim 9, further comprising: meansfor receiving bandwidth requests from the modems; means for granting thebandwidth requests, wherein the grant includes the assigned data IUC;and means for processing data from received bursts using parameters fromthe assigned data IUCs for each of the modems sending data in theupstream channel.
 11. The system of claim 10, further comprising meansfor changing the data IUC for any modem to adapt to changes in themodem's SNR and/or codeword error rate.
 12. The system of claim 10,further comprising means for changing an assigned data IUC for any oneof said modems to adapt to changes in measured SNR and/or codeword errorrate.
 13. The system of claim 10, further comprising means fordetermining the number of mini-slots needed prior to granting saidrequest for bandwidth.
 14. The system of claim 9, wherein said burstparameters include modulation type, forward error correction (FEC)coding type, and FEC rate.
 15. The system of claim 9, wherein each ofsaid data IUCs has a unique parameter set.
 16. An upstream modulationsystem for broadband communications, comprising: means for definingburst parameters associated with a range of data interval usage codes(IUCs); means for monitoring signal-to-noise ratio (SNR) for modems in anetwork; and means for dynamically assigning the data IUCs to the modemswithin an upstream channel according to the modem's SNR to enable eachof the modems in the upstream channel to achieve bandwidth efficiencyduring upstream data transmissions.
 17. The system of claim 16, furthercomprising: means for receiving bandwidth requests from the modems;means for granting the bandwidth requests, wherein the grant includesthe assigned data IUC; and means for processing data from receivedbursts using parameters from the assigned data IUCs for each of themodems sending data in the upstream channel.
 18. The system of claim 17,further comprising means for changing the data IUC for any modem toadapt to changes in the modem's SNR.
 19. The system of claim 17, furthercomprising means for changing an assigned data IUC for any one of saidmodems to adapt to changes in measured SNR.
 20. An upstream modulationsystem for broadband communications, comprising: means for definingburst parameters associated with a range of data interval usage codes(IUCs); means for monitoring codeword error rates for modems in anetwork; and means for dynamically assigning the data IUCs to the modemswithin an upstream channel according to the codeword error rate toenable each of the modems in the upstream channel to achieve bandwidthefficiency during upstream data transmissions.
 21. The system of claim20, further comprising: means for receiving bandwidth requests from themodems; means for granting the bandwidth requests, wherein the grantincludes the assigned data IUC; and means for processing data fromreceived bursts using parameters from the assigned data IUCs for each ofthe modems sending data in the upstream channel.
 22. The system of claim21, further comprising means for changing the data IUC for any modem toadapt to changes in the modem's codeword error rate.
 23. The system ofclaim 21, further comprising means for changing an assigned data IUC forany one of said modems to adapt to changes in measured SNR and/orcodeword error rate.